In part 1, I showed you a long-nose crankshaft that I sourced for my miata’s engine rebuild. Well… I’m no longer planning to rebuild my original motor. I found a 90-93 block + head on facebook market place for $120. It’s not in the greatest condition, but I think it’s salvagable.
I bought the motor from a father and son. The son didn’t want to fess up to how the motor had spun two rod bearings (I think he was hooning around in the car and didn’t want to say with his dad there). The motor doesn’t have an oil pan, but I’ll have to swap my oilpan over anyways since I have the turbo oil drain installed. Did you know that miata oilpans are selling for nearly $200 on ebay??? Makes me wish I would have taken the oilpan from the junker motor I found in part 1 and sold it. It could have recouped the cost of the whole engine! I digress.
Inspecting the Crankshaft
Here are some photos of the crankshaft journals. You can see that the #4 and #3 rod journals are the most torn up from the spun bearings.
I measured the crank journals and compared them to Mazda’s factory tolerances. The main journals look within spec, but the crankpin journals might need to be reground to fit 0.25mm undersize bearings. You can see that the #4 and #3 crankpin journals are loose in the ‘Y’ direction. I think the ‘Y’ direction is where the majority of the forces get applied, so it probably sees the most wear. When I take my parts to get machined, I’ll probably take both cranks and see which one they think is worth using.
Inspecting the Bearings
The motor came with a box full of parts that they pulled off when they tore it down. I have all the original pistons and rods; they look fine. I dug around in the box and found most of the bearings. I’m missing one pair of rod bearings, but from what I have you can tell the rod bearings definition took most of the damage.
Misc
Just some other photos…
Next: Part 3 - Head Teardown
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